Optical systems are used for a variety of purposes. A typical use is for telescopic viewing, to enlarge the image of a distant object. Telescopes, binoculars, microscopes and aiming sights for firearms, weapons, cameras, and surveying transits, are well known examples of optical systems which achieve image enlargement. Other optical systems create image reduction, such as the lenses of a camera. Still other optical systems achieve only a viewing advantage, such as periscopes for observations of experiments or for surveillance and optical inspection systems for underwater or unaccessible location viewing.
The most common optical system is formed by a number of optical lenses separately spaced at predetermined positions along an optical axis. The position and shape of the lenses achieve the desired image enlargement, image reduction or other optical effect. The optical effect occurs as a result of light refraction occurring at the surface of the lens where the lens interfaces with another different refractive medium adjacent to the lens. The other medium is usually air or a different type of glass.
The common lens and air gap construction of optical instruments has resulted in certain disadvantages and drawbacks. The clarity of vision through the optical system depends on the ability to maintain fixed positions of the lenses along the optical path. A mechanical housing, tube or other structure is normally employed to hold the lenses at these fixed positions. However, the mechanical structure is subject to changes in dimensions due to rough handling, thermal effects and mechanical distortion, thereby diminishing the desired optical effect. Furthermore, moisture in the air between the lenses in a closed housing may condense on the lenses in certain humidity and temperature conditions, thereby fogging the lenses.
The mechanical problems of maintaining the lens positions have been solved by using strong mechanical lens housing structures which are generally bulky and heavy. While these types of mechanical structures are usually effective, the weight and size of the housing structures creates drawbacks. For example, heavy binoculars and hand held telescopes are often difficult to hold steady for extended time periods. Additionally, hunters and soldiers find the added weight and bulk of a telescopic sight on a firearm increases the difficulty of carrying and manipulating the firearm.
The problem of lens fogging has been solved by hermetically sealing the optical instrument housing and filling the spaces between the lenses with dry nitrogen gas. The nitrogen gas prevents the ambient humidity from entering the housing. Without moisture in the housing there is no moisture to condense. The long term viability of the nitrogen gas solution depends on the ability of the housing to contain the gas. The seals and the other mechanical aspects of the sight may allow the nitrogen gas to dissipate and be replaced with ambient humidity over time. Furthermore the seals and other confinement structures contribute to the weight, size, fragility and complexity of the optical instrument.
Another limitation of any telescopic optical instrument is that its effectiveness is directly related to the level of the ambient light. To achieve perceptible magnification levels, it is necessary that adequate light illuminate the object being viewed. An increase in magnification has the effect of diminishing the amount of light perceived by the user. Thus if the object viewed is inadequately illuminated, the magnified object will not be seen clearly. It is for this reason that microscopes frequently include auxiliary light sources to augment the ambient light, thereby allowing adequate perception of the object being viewed. In general, however, optical instruments themselves are typically incapable of enhancing the light energy of the magnified object.
It is with respect to these and other background considerations, limitations and problems, that the optical instrument of the present invention has evolved.